Why would you want to do a thing like that? I can see doing it if you had smaller tires on there, but with larger tires your actually putting less miles on your car. They do have things that show true speed. Just remember what the differance is to a % eventually you won't even have to think about it you just know that 50 mph = 55mph and 60 =66 or however your size tires work out compared to stock (29" or 29.5"). Point being don't spend money you don't need to.